US 4,376,968 AGranted

Protection system for immunizing an inverter system against A-C line voltage disturbances

AssigneeBorg-Warner Corporation

InventorsRussel P. Wueschinski, Edward C. Siemon

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Abstract

When a-c power line voltage is rectified by a phase-controlled SCR rectifier bridge to develop an adjustable d-c bus voltage which is then converted by an inverter back to a-c for driving a load, such as a motor, line voltage disturbances, resulting from momentary power outages or major power reductions, will have a deleterious effect on the operation of the inverter system. Such disturbances will cause improper firing of the SCR's and the d-c bus voltage may increase considerably, disrupting the normal operation of the inverter system and possibly destroying the switching devices in the inverter. Immunization against the effects of the line voltage disturbances is obtained by shutting down or disabling the phase-controlled SCR rectifier bridge anytime such a disturbance occurs. In this way, while the output voltage of the rectifier bridge is effectively interrupted during the occurrence of each line voltage disturbance, the inverter will continue to operate in near normal manner in response to the d-c voltage provided by the filter capacitor. At the conclusion of each disturbance, the operation of the rectifier bridge will be slowly restored to normal to avoid overshoot of the d-c bus voltage.

Claims6

Dependent claims

A controlled d-c power supply for rectifying applied a-c power line voltage to develop therefrom a d-c bus voltage of a desired magnitude for application to an inverter, the a-c line voltage being subject to unwanted disturbances caused by momentary power outages or major power reductions, comprising:

a phase-controlled SCR rectifier bridge, having at least two SCR's, for rectifying the a-c line voltage to produce d-c bus voltage of a magnitude determined by the conduction angle of the SCR's during each half cycle of the a-c power line voltage;
pulse generating means, responsive to a reduced amplitude replica of the a-c line voltage, for developing a ramp-shaped pulse during each half cycle of the a-c line voltage and including a band-pass filter for attenuating, in the reduced-amplitude replica of the a-c line voltage, frequencies above and below the voltage's fundamental frequency;
control means for utilizing the ramp-shaped pulses to trigger said SCR's into conduction at a desired phase angle, following the beginning of each half cycle of the a-c line voltage, thereby to control the conduction angle in order to establish the d-c bus voltage at a selected desired amplitude level;
sensing means which compares the input and output signals of said band-pass filter in order to detect the unwanted disturbances in said a-c line voltage caused by momentary power outages or major power reductions;
and disabling means, controlled by said sensing means, for turning said SCR's off during the occurrence of each unwanted disturbance, thereby rendering the d-c power supply immune to such disturbances.

2 more elements

Dependencies are inferred from the claim text.